Plant to control the section area of a rolled product and corresponding method

ABSTRACT

A plant to control the section of a rolled product passing through a rolling train comprises at least two rolling stands, at least a section area measurer disposed immediately at exit from at least one of the stands located downstream of the first stand, a control unit comprising a database, in which at least the parameters relating to the expected value of the section of the rolled product at exit from each stand are memorized, means to compare the values detected by the section area measurer with the values memorized in the database and means to act on the rolling parameters according to said values detected.

FIELD OF THE INVENTION

The present invention concerns a plant and the corresponding method to control the section, and in particular its area, of a rolled product worked in rolling mills.

In particular, the present invention is applied in a rolling line to control and adjust the drawing action or thrust imparted to the rolled product, in order to guarantee that the dimensional values of the final product are respected and to guarantee high quality characteristics of the material.

BACKGROUND OF THE INVENTION

It is known that, in a rolling line consisting of at least two rolling stands, or a single stand where there are two or more blocks of rolling modules combined, between the two stands or between the two rolling blocks a drawing action is determined which is difficult to control on the segment of the rolled product, and which can generate traction or thrust actions that can modify the section area of the rolled product, leading to a final product that does not conform to the required specifications.

For this reason solutions are known in which interstand measurers are provided, which detect the drawing action produced on the rolled product between two adjacent rolling stands or blocks, examples of which are described in the European patents EP 756906 and EP 756907, in the name of the present Applicant.

This problem of controlling the section in relation to the variations in drawing action is particularly important in the case of sections of 70 mm and more, where there is the additional problem that, when the tail end of the rolled product leaves the first stand, uncontrolled deformations occur which lead to unacceptable variations in section, and hence the need to discard long segments of bar that do not meet the required tolerances.

In general, an irregular and/or inconstant drawing action over time can lead to dimensional irregularities and/or to unacceptable deteriorations in quality, which can cause losses in production, stoppages of the rolling line, need for frequent adjustments and other problems that influence the efficiency and productivity of the line.

In the state of the art there are various methods for controlling the drawing action in rolling plants.

Document EP-A1-920.926, also in the name of the present Applicant, discloses a method to control the drawing action applied between a semi-finishing rolling block and a finishing rolling block. The method provides to use three section detectors, one at exit from the semi-finishing rolling block, one at entrance to the finishing rolling block and one at exit from the finishing rolling block. The values obtained by said detectors are compared with expected values memorized in suitable databases, and in the event of discrepancies a correction is carried out in the drawing parameters of the rolled product.

However, this document performs a control of the drawing action by detecting one dimensional parameter at exit from a semi-finishing block and by comparing it with the value at entrance to a finishing block and with the value at exit from the finishing block itself In the event of divergences from the expected values, a correction is generated which in any case does not prevent the discard of a large quantity of material, which is unacceptable in the case of large diameter profiles.

As we said, an interstand control is known, according to which the drawing action is controlled and consequently adjusted so as to keep it constant, or almost constant, within predetermined limits also as the physical and/or chemical condition of the material passing through varies.

However, this known method is valid in the case of rolled products with small section or thickness, but becomes progressively less effective and less reliable in the case of progressively bigger sections. In particular, already in the case of sections with a diameter of about 70 mm, or up to 100 mm depending on the type of steel and the working temperature, it becomes such as to generate an incorrect rolling, and hence the phenomenon intensifies for even bigger sections.

Furthermore, an imprecise and inconstant control of the drawing action does not allow to perform adjustments on the line such as to allow to keep the process automated and repeatable, irrespective of conditions upstream, maintaining determinate dimensional tolerances, without having recourse to complex and complicated adjustments that would cause stoppages of the rolling line and a reduction in production.

Purpose of the present invention is therefore to obtain a plant, and the corresponding method, which are able, in every rolling condition, in particular when rolling products with a section diameter from about 70 mm and more, to provide a control of the section area in every part of the rolled bar, in order to obtain a final product that is coherent with the expected sizes.

The Applicant has devised, tested and embodied the present invention to overcome these problems and to obtain a control of the section of the rolled product that is efficient and effective along the whole rolling line.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purpose, a plant according to the present invention, which overcomes the limits of the state of the art and eliminates the defects present therein, is used to control the section area of a rolled product passing through a rolling train comprising at least two rolling stands.

As we said above, the invention is applied in particular on products with a diameter from 70 mm and more, since in such cases the problems involved are more significant.

According to a main characteristic of the present invention, the plant comprises a device to measure the section area, or section measurer, disposed immediately at exit from one of the rolling stands, which can be the last stand in the case of a train with only two stands, or an intermediate stand when the train comprises three or more stands.

In any case, the section measurer will detect the size of the section area of a round profile, or similar to round, so that, in the case of a train with a larger number of stands, the measurer will be disposed at exit from a stand identified by an even number (2̂, 4̂, 6̂ etc.), while at exit from the stands identified by an odd number (1̂, 3̂, 5̂) the section of the bar will be oval.

The section measurer therefore controls the dimension of the round section of the rolled product exiting from the corresponding rolling pass.

According to another characteristic of the present invention, the plant comprises a control system comprising a control unit, inside which is contained a database of parameters necessary for the correct working, to which the section measurer is connected.

According to a variant, the database contains a series of working parameters, for example the size of the diameter of the rolled product exiting at least from each rolling stand in which a round section is obtained, correlated to other working parameters, for example the temperature of the rolled product, the type of steel, the rolling speed, the data relating to the wear of the rolling rolls, and other. In this way, the rolling line can be set, for example in terms of the gap between the rolling rolls, at the start of the cycle as a function of parameters set in advance, or detected instantaneously, for example by temperature probes disposed at entry to the rolling line, by speed detectors or other.

According to the invention, the value of size detected by the section measurer is compared with the value of the section area, memorized in the above-mentioned database, which the rolled product should have at exit from the stand where the detection is made, possibly based on the set or pre-memorized working parameters.

If dissimilarities are found, either negative or positive, that is, plus or minus, between the value detected of the section and the expected pre-memorized value, the control system acts on the rolling speed, that is, on the speed of rotation of the rolls of at least one of the stands, between the one provided with the measurer and one or more of those upstream thereof, in order to modify the drawing action and return the section size to the expected value.

Since the dissimilarity between the value detected and the value expected can be positive or negative, that is, the section area detected can be greater or less than the expected and pre-memorized one, the value of the drawing action can be correspondingly increased or decreased. In particular, sections with a diameter of 70 mm and more, up to 100 mm and more, can be subjected in the segment between the two stands, both to a greater drawing action and to a greater thrust, in order to return the value of drawing action to the value corresponding to the desired section, within the admissible limits of the peak load for the segment of rolled product in the interstand.

According to a variant, the control system and its database can be equipped with self-learning systems which, based on the adjustments made during one rolling cycle, memorize the values of speed and possibly the gap between the rolls, so that when a new cycle is started, if the starting conditions are the same (starting diameter of the bar, type of material, temperature, etc.) the rolling line, and in particular all the stands, is already in a substantially optimum situation for the rolling passes.

According to the invention, a situation may occur in which the correction of the drawing action between two stands may not be sufficient to return the section of the rolled product to the expected value. In this case, the invention provides a first option in which the correction of the drawing action is distributed over several stands, if present, or over several pairs of stands between those upstream of the stand where the section measurer is disposed at the exit.

In a further evolution, if the dissimilarity in the section cannot be corrected only by adjusting the drawing action, the invention provides to intervene by widening or reducing the gap of one or more of the stands involved in detecting the size.

According to another form of embodiment of the invention, a maximum threshold is provided of the drawing action admissible between two or more stands, so that, when the tail end of the bar leaves the first stand, the consequent annulment of the drawing action cannot cause the size of the section to go outside acceptable and controllable values, which would thus oblige a considerable part of the terminal segment of the rolled bar to be discarded.

According to a variant, in the case of four rolling stands, the section measurer can be located either downstream of the second stand or downstream of the fourth stand. In this case, it is possible to proceed with a rough adjustment between the first and second stand and with a fine adjustment between the third and fourth stand, always within the maximum admissible threshold of drawing action or thrust on the rolled product being worked.

According to another variant, a control is carried out on the characteristics (for example temperature, section size, type of material, etc.) of the rolled product arriving in the upstream stand, so as to proceed, before the corresponding rolling pass, with the necessary settings of the work parameters of the stand, so as to obtain the desired drawing action and such to take the rolled product to a section size that corresponds to the expected and pre-memorized value.

DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of one form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

FIG. 1 shows schematically a rolling train consisting of four rolling stands, in which the method according to the invention is applied between the third and fourth stand;

FIG. 2 shows a variant of FIG. 1;

FIG. 3 shows another variant of FIG. 1;

FIG. 4 is a schematization of the functioning of the invention.

DESCRIPTION OF ONE FORM OF EMBODIMENT

In the drawings, identical parts or functions have the same reference numbers.

FIGS. 1, 2 and 3 show by way of example a rolling train 30 consisting of four rolling stands 11, considering an oval-round-oval-round rolling cycle, in which a rolled product 12 is deformed through each stand 11, assuming an oval and round cross section in alternate sequence. In this way better quality characteristics of the final product are obtained.

The invention also concerns the case where there are two, six or more stands 11.

The four stands 11, respectively 11 a, 11 b, 11 c and 11 d in this case are identified for a final round rolling, so they are characterized by the acronyms O1 and O2 to indicate oval rolling and by T1 and T2 to indicate round rolling.

Each of the stands 11, in a known manner, has a motor 14 to move the parts needed for rolling, in particular to rotate rolling rolls 18, and adjustment means 15 to adjust the calibration gap between the rolling rolls 18.

In the case of FIGS. 1 and 2, a section measurer 10 is provided at exit from the last stand 11 d, that is, the fourth.

In the case of FIG. 1, the invention is applied only between stands 11 c and 11 d of the O2 and T2 type. The adjustment of the drawing action, based on the measurements of the section area performed by the section measurer 10, is applied only between the third stand 11 c and the fourth stand 11 d.

In the case of FIG. 2, the invention is applied between all four stands 11 a, 11 b, 11 c and 11 d, distributing the adjustment of the drawing action so that a dissimilarity between the expected value of the section area and the value measured by the section measurer 10 is corrected by adjusting the drawing action between all said stands 11 a, 11 b, 11 c and 11 d.

In FIG. 3 a section measurer 110 is provided at exit from the second stand 11 b and a section measurer 10 at exit from the fourth stand 11 d.

In this case, if the section measurer 110 already detects a dissimilarity between the expected value of the section area and the section area measured, this solution allows to intervene by adjusting the drawing action between the stands 11 a and 11 b, and then possibly intervening also with an adjustment of the drawing action between stands 11 c and 11 d.

It is possible, according to the invention, to provide that, based on the information obtained by the section measurer 10, the drawing action is controlled and adjusted also between the second stand 11 b and the third stand 11 c.

As well as the adjustment of the drawing action itself, the invention provides that, according to the circumstances, it is possible or necessary to intervene on the calibration gap between the rolling rolls 18, acting on each occasion on the motor 14 or on the adjustment means 15 of one or more stands 11.

In particular, this happens when the dissimilarity between the expected value and the detected value of the section area of the rolled product is too great to be corrected by adjusting the drawing action or thrust contained within acceptable limits, also taking into account an adjustment distributed among several stands, or among all the stands.

In this way, the control system can provide an adjustment of the gap between the rolling rolls 18, for example of the last stand 11 d or the last two stands 11 c and 11 d, together with an adjustment of the drawing action between said two stands, until the section measurer 10 detects that the value of the section area corresponds to the expected value memorized in the control system.

A maximum threshold of drawing action or thrust is also provided, acceptable between two stands, so that said value is not excessive when the tail end of the rolled product 12 leaves the first stand 11 a, something which in this case could lead to an unacceptable deformation, both in the sense of stretching (excess drawing action), and also in the sense of deformation and compression (excess thrust), of the last segment of the rolled product 12 which would thus have to be discarded.

FIG. 4 shows the invention schematically with a block diagram, describing the functioning thereof, as described hereafter.

The section measurer 10 (or section measurers 10 and 110) detects the section area of the rolled product 12 and transmits the data detected to a control unit 20, which can be the programmable type.

The control unit 20 contains a database 21, in which the parameters necessary for controlling the rolling are memorized, and in particular at least the values relating to the value of the section area of the rolled product 12 at exit from each of the stands 11 a, 11 b, 11 c, 11 d. With the aid of the database 21, the control unit 20 controls whether a possible variation in the section area, detected by the section measurer 10, 110, differs or not from the expected value.

The adjustments performed at the end of the rolling cycle can be memorized in the database 21, so as to allow to set the settings of all the stands 11 a-11 d to start the following cycle if the product to be rolled has the same characteristics as the product already rolled, thus also obtaining an optimum setting already on the first segment of the rolled product 12.

Furthermore, rolling cards can be present in the database 21, in which the setting value of the speed of rotation of the rolls and/or the gap between the rolls is correlated to data relating to the wear of the rolls and to specific characteristics of the rolled product 12 being worked, for example its temperature at entry into the rolling line, the type of steel, the starting diameter of the rolled product 12 and other.

At entry to the rolling line there can be temperature, speed and/or diameter detectors (not shown), which detect the instantaneous values and allow, by means of the control unit 20, to set automatically the settings of the stands 11 a-11 d depending on the detections performed.

In order not to require continuous adjustments during working, a control device 23 is provided of the characteristics of the rolled product 12 being worked (temperature at entry to the rolling line, type of steel, starting diameter of the rolled product 12), on arrival in the upstream stand 11, so as to proceed with the settings of the stand itself that are necessary to obtain a constant or almost constant section area.

Depending on the control performed by the control unit 20, the following happens.

If the detection made by the control unit 20 does not give any anomalies, that is, if the value detected by the section measurer 10 corresponds substantially to the expected value, also in relation to the possible instantaneous values of temperature, speed, diameter, etc., performed at entry to the line, a confirmation block 24 allows the rolling to proceed without the control unit 20 intervening.

If the control unit 20 detects an incorrect value, the control unit 20 intervenes by means of an adjustment block 25, adjusting the speed of the motor 14 that feeds the rolling rolls 18 by an action performed on a motor adjustment block 26, or by adjusting the gap, that is, the distance between the rolling rolls, by means of the adjustment means 15 and following a gap adjustment block 27, with actions of an entity coherent with the information relating to the product being rolled and contained in the database 21.

It is clear that modifications and/or additions of parts may be made to the plant as described heretofore, without departing from the field and scope of the present invention. 

1. Plant to control the section area of a rolled product (12) passing through a rolling train (30) comprising at least two rolling stands (11 a, 11 b, 11 c, 11 d) equipped with rolling rolls (18), used in particular for products with a section from 70 mm and more, characterized in that it comprises: a section area measurer (10) disposed immediately at exit from at least one of the even stands (second, fourth, sixth, etc.) located downstream of the first stand (11 a) and configured to measure the section area of a round profile; a control unit (20) comprising a database (21), in which at least the parameters relating to the expected value of the round section of the rolled product (12) at exit from each stand are memorized, and comprising means to compare the values detected by the section area measurer (10) with the values memorized in said database (21); wherein, in the event of dissimilarity between the above-mentioned values, said control unit (20) comprises means to act on at least the motors (14) associated with said rolling rolls (18) in order to vary the rotation speed of said rolling rolls (18) so as to modify, either to increase or decrease, the drawing action or thrust between at least two of said stands (11 a, 11 b, 11 c, 11 d) so as to return the value of the section of the rolled product (12) to the expected value.
 2. Plant as in claim 1, characterized in that said control unit (20) comprises means to also act on adjustment means (15) of the calibration gap between said rolling rolls (18), said means being able to be activated when said modification of the drawing action or thrust between the stands is not able alone to bring the values measured of the section to the values expected.
 3. Plant as in claim 1, characterized in that said section area measurer (10) is disposed at exit from the last rolling stand (11) of said rolling train (30).
 4. Plant as in claim 1, characterized in that said section area measurer (10) is disposed at exit from one or more intermediate rolling stands (11) of said rolling train (30).
 5. Plant as in any claim hereinbefore, characterized in that a device (23) to control the characteristics of the rolled product (12) arriving at a rolling stand is associated with said control unit (20).
 6. Method to control the section of a rolled product (12) in a rolling train (30) comprising at least two rolling stands (11 a, 11 b) equipped with rolling rolls (18), used in particular for rolled products (12) with a diameter from 70 mm and more, characterized in that it comprises: a first step in which a section area measurer (10), disposed at exit from at least one of the even stands (second, fourth, sixth, etc.) located downstream of the first stand (11 a), detects the size of the section area of the rolled product (12) exiting from the corresponding rolling pass; a second step in which a control unit (20), comprising a database (21) in which at least the parameters relating to the value of the section area of the rolled product (12) at exit from each stand are memorized, compares the values detected by the section area measurer (10) with the values memorized in said database (21); a third step in which, in the event of dissimilarity between the above-mentioned values, said control unit (20) acts on at least the motors (14) associated with said rolling rolls (18) in order to vary the rotation speed of said rolling rolls (18) so as to modify, either to increase or decrease, the drawing action or thrust between at least two of said stands (11 a, 11 b) so as to return the value of the section to the expected value.
 7. Method as in claim 6, characterized in that, in the event that the dissimilarity between the expected value of the section area and the value measured is great, it provides a step in which the adjustment of the drawing action or thrust is partialized and distributed over all the stands of the rolling train.
 8. Method as in claim 6 or 7, characterized in that in the event that the dissimilarity between the expected value of the section area and the value measured is great, it provides to intervene in the adjustment of the gap of at least one of the rolling stands (11 a, 11 b, 11 c, 11 d), so as to return the value of the section area of the rolled product (12) to the expected value.
 9. Method as in claim 6, characterized in that it provides to define an acceptable maximum value of the drawing action or thrust in relation to a condition where the tail end of the rolled product (12) is released with respect to at least the first rolling stand (11 a).
 10. Method as in any claim from 6 to 9, characterized in that it provides that in said database (21) values of the section area of the rolled product (12) at exit from at least some of the rolling stands (11 a-11 d) are memorized, in relation to one or more of its temperature, speed or diameter.
 11. Method as in claim 10, characterized in that it provides to detect the values of one or more of its temperature, speed or diameter at the entrance of the rolled product (12) into the rolling line and to select inside said database (21) the comparison values to be used in the adjustment carried out along the rolling line. 